Communication method, mobile network system and device

ABSTRACT

A mobile terminal (UE) used in a mobile communication network that includes a mobility management entity (MME) and a serving gateway (S-GW), receives paging from the mobile communication network, upon arrival of an incoming call destined for the mobile terminal at the mobile communication network, in which if the mobility management entity has restarted, the serving gateway maintains a specific S5/S8 bearer and deletes other bearers, and in response to the paging, re-attaches to the mobile communication network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of co-pending application Ser. No.13/381,746 filed on Dec. 30, 2011, which is a National Stage ofInternational Application No. PCT/JP2011/060215 filed on Apr. 27, 2011,which claims foreign priority to Japanese Patent Application No.2010-102166 filed on Apr. 27, 2010. The total contents of disclosure ofthe Patent Application of the senior filing date are to be incorporatedby reference into the present Application.

TECHNICAL FIELD

This invention relates to a communication network and, moreparticularly, to a system and a method as well as an apparatus that maybe applied to advantage to the next-generation mobile network system EPC(Evolved Packet Core).

The following recites certain abbreviations used in the presentspecification.

-   CS: Circuit Switched-   CSFB: Circuit Switched Fall Back-   eNodeB (eNB): evolved NodeB-   G-MSC: Gateway Mobile Switch Center-   GPRS: General Packet Radio Service-   GTP-C: (GPRS Tunneling Protocol Control Plane)-   GTP-U: (GPRS Tunneling Protocol User Plane)-   P-MIP: Proxy Mobile Internet Protocol-   HSS: Home Subscriber Server-   IMS: IP Multimedia Subsystem-   IMSI: International Mobile-Station Subscription Identifier-   ISR: Idlemode Signaling Reduction-   LTE: Long Term Evolution-   MME: Mobility Management Entity-   MSC: Mobile Switching Center-   MTC: Machine type communication-   P-GW: (PGW or PDN-GW): Packet Data Network Gateway-   PDN: Packet Data Network-   QCI: QoS Class Identifier-   RAI: Routing Area Identity-   RNC: Radio Network Controller-   S-GW (or SGW): Serving Gateway-   SGSN: Serving GPRS Support Node-   SMS: Short Message Service-   SCPT: Stream Control Transmission Protocol-   TA List: Tracking Area List-   TAU: Tracking Area Update-   TEED: Tunnel Endpoint Identifier-   GRE key: Generic Routing Encapsulation Key-   UE: User Equipment-   UMTS: Universal Mobile Telecommunications System-   VLR: Visited Location Register-   3G: Third Generation-   3GPP: 3rd Generation Partnership Project

BACKGROUND

The next-generation mobile network system EPC is a network architecturethat accommodates 3G (third generation mobile phone communicationsystem), LTE and so forth in one network. The following describesseveral network nodes.

A MME is a mobility management node. In LTE radio access, the MME takescharge of mobility management (mobility control), such as tracking, ofan idle-mode mobile station (UE), authentication and setting up a userdata forwarding path between an S-GW and a base station (eNodeB), in LTEradio access. The mobile station (UE) is also termed ‘a user apparatus’,‘a mobile terminal’ or simply ‘a terminal’. The MME is involved intracking and paging of idle-mode UEs or in bearer activate/deactivateprocesses. The MME selects the S-GW at the time of handover of the UE inLTE and performs user authentication along with HSS. It is noted that abearer means a logical packet transmission path set up between eNodeBand S-GW/P-GW or the like.

An SGSN is a mobility management node in the 3G core network. It is apacket switching unit that takes charge of mobility management for theUEs, such as serving subscriber management, serving subscriber mobilitymanagement, originating/incoming call control, tunneling control,charging control, QoS (Quality of Service) control or the like.

When the UE is in an idle or power-saving state (LTE-idle) in an LTEcore network, the UE is identified at the accuracy corresponding to atracking area list (TA List) composed of a plurality of cells (MMEmaintains the latest updated TA List). At the time of an incoming callto the mobile station, paging is performed using the latest TA Listregistered last time. The SGSN of the 3G core network performs paging inan RA (Routing Area).

An S-GW performs routing and forwarding of a user data packet. The S-GWis a bearer management node that manages context of the UE (a parameterof IP bearer service or the like). In response to a bearer settingrequest from an MME that has received an attach request from the UE, TheS-GW sets a path setting request for a P-GW and bearer in the directionof an eNode. The S-GW also performs triggering of a paging when thedownlink (DL) data to a terminal has arrived.

A P-GW takes charge of connection of the UE to a packet data network (aservice network: Web browsing service or an external network, such asIMS or the like.

The following describes restarting of MME/SGSN.

The ‘restart’ or ‘restart of MME/SGSN’ means cessation of service due tofailure, or intentional cessation of service for maintenance, that leadsto initialization setting operation in the MME/SGSN, as a result ofwhich, subscriber information or hearer information that is necessaryfor the MME/SGSN operation to operate is lost.

Non-Patent Document 2 (3GPP TS 23.007) provides that, when the S-GWdetects that the MME /SGSN has restarted, the S-GW is to release bearercontext of the UE registered in the MME/SGSN that has restarted. Thatis, According to Non-Patent Document 2, when the MME re-starts afterfailure, the MME removes the entirety of bearer contexts affected by therestarting. When the S-GW detects that the MME has restarted, the S-GWremoves PDN connection table/bearer context corresponding to the MMEthat has restarted and releases inner resources relevant to the PNDconnection.

Assuming that an S-GW operates in accordance with the abovespecification of the Non-Patent Document 2, when the MME operation hasrestarted, the S-GW is unable to effect a packet incoming operation tothe UE until originating a call by the mobile station itself or periodiclocation registration (e.g., Attach/TAU Request) periodically byperformed by the UE itself to the MME.

When there is an incoming call to the UE, the network performs pagingall at once to whole cells associated with an area where the UE has madelocation registration (tracking area). The so paged UE accesses aserving cell and establishes a call. However, according to thespecification of Non-Patent Document 2, the entirety of bearerinformation or resources of the restarted MME has already been removedor released. That is, in the S-GW, radio access hearers in the directionof from the S-GW to the eNodeB and session information between the MMEand the S-GW have been removed or released, so that when the incomingpacket data to the UE is received only to no effect.

In the S-GW in this state, TEID or GRE Key, as the identificationinformation of a tunnel (GTP-U or P-MIP), a transport protocol betweenthe S-GW and the P-GW, also has been removed. Hence, in the S-GW, theincoming data is rejected. The P-GW also removes relevant resources inresponse to the rejection of the incoming packet data from the S-GW.

Non-Patent Document 1:

-   3GPP TS 23.203 V9.4.0 (2010-03) 3rd Generation Partnership Project:    Technical Specification Group Services and System Aspects: Policy    and charging control architecture (Release 9), page 31, Table 6.1.7:    Standardized QCI characteristics    Non-Patent Document 2:-   3GPP TS 23.007 V9.3.0 (2010-03) 3rd Generation Partnership Project:    Technical Specification Group Core Network and Terminals;    Restoration procedures (Release 9), pages 27-28    Non-Patent Document 3:-   3GPP TS 23.272 V9.3.0 (2010-03) 3rd Generation Partnership Project:    Technical Specification Group Services and System Aspect; Circuit    Switched (CS) fallback In Evolved Packet System (EPS); Stage 2    (Release 9) pages 26-27

SUMMARY

The disclosures of the Non-Patent Documents 1 to 3 are incorporated byreference into the present specification. The following is an analysisof the related techniques.

In case the S-GW operates in accordance with the above specification ofNon-Patent Document 2, as described above, the S-GW which has detectedthe restarting of the mobility management node MME/SGSN releasesentirety of hearers of the UE registered in the MME/SGSN whererestarting occurred.

Hence, the incoming to the UE after the restarting of the mobilitymanagement node MME/SGSN may not be informed to the UE until such timethe attach operation for registration in the network is carried out inthe UE. That is, if, during the time that elapses after restarting ofthe MME/SGSN until the end of the attachment operation, triggered by theorigination by the UE itself or the periodic location registration bythe UE, the UE is unable to have a communication service, even if thereis an incoming of the communication service. For example, during a timeinterval of the periodic location registration (TAU request) (e.g., upto 45 minutes), following the restarting of the MME/SGSN, incomingpacket data, addressed to the UE, may not be delivered to the UE.

That is, a packet communication service is at a standstill. This poses aserious problem since communication services as social infrastructuremay not be received for a preset time in case IMS is exploited on an EPSnetwork.

Accordingly, it is an object of the present invention to provide asystem, a method and an apparatus which enable to accelerate restorationof communication services for a mobile terminal (UE) after restarting ofa mobility management entity (MME).

In accordance with one aspect of the present invention, there isprovided a mobile terminal (UE) used in a mobile communication networkthat includes a mobility management entity (MME) and a serving gateway(S-GW), the mobile terminal comprising:

-   -   a receiver that receives paging from the mobile communication        network, upon arrival of an incoming call destined for the        mobile terminal at the mobile communication network with the        serving gateway, upon restarting of the mobility management        entity, maintaining a specific S5/S8 hearer, while deleting        other bearers; and

a transmitter that in response to the paging, re-attaches to the mobilecommunication network.

In accordance with one aspect of the present invention, there isprovided a communication method in which a bearer management nodemaintains a specific bearer eligible for restoration of communicationservices, and removes the other bearers. In case a mobility managementnode is restarted, the hearer management node maintains at least onebearer.

In accordance with another aspect of the present invention, there isprovided a method for registration of a mobile terminal (UE) in a mobilecommunication network that includes a mobility management entity (MME)and a serving gateway (S-GW), the method comprising:

receiving, by the mobile terminal, paging from the mobile communicationnetwork, upon arrival of an incoming call destined for the mobileterminal at the mobile communication network with the serving gateway,upon restarting of the mobility management entity, maintaining aspecific S5/S8 bearer, while deleting other bearers; and

re-attaching to the mobile communication network, by the mobileterminal, in response to the paging.

In accordance with another aspect of the present invention, there isprovided a communication method wherein, on restarting of a mobilitymanagement node, a circuit switched node sends to the mobilitymanagement node a notification message including identificationinformation associated with the UE and location registration areainformation, and the mobility management node starts paging, inclusiveof the identification information associated with the UE, for an areacorresponding to the location registration area information.

According to the present invention, there is also provided a mobilenetwork system in which a hearer management node maintains a specifichearer eligible for restoration of communication services, and removesother hearers. The mobile network system includes a mobility managementnode and a hearer management node. When restarting of the mobilitymanagement node is performed, the bearer management node maintains atleast one of the bearers as set.

According to the present invention, there is provided a mobile networksystem comprising a mobility management node and a circuit switchednode. In case restarting of the mobility management node is performed,the circuit switched node sends to the mobility management node anotification message inclusive of the identification informationassociated with the UE and the location registration area information.The management node performs paging including the identificationinformation associated with the UE for an area corresponding to thelocation registration area information.

According to the present invention, there is provided a node apparatusthat manages a bearer, wherein the node apparatus maintains a specificbearer eligible for restoration of communication services, and removesother bearers. In case restarting of the mobility management node isperformed, the node apparatus maintains at least one of the bearers asset.

According to the present invention, it is possible to acceleraterestoration of a communication service for a mobile station followingrestarting of a mobility management node.

Still other features and advantages of the present invention will becomereadily apparent to those skilled in this art from the followingdetailed description in conjunction with the accompanying drawingswherein only exemplary embodiments of the invention are shown anddescribed, simply by way of illustration of the best mode contemplatedof carrying out this invention. As will be realized, the invention iscapable other and different embodiments, and its several details arecapable of modifications in various obvious respects, all withoutdeparting from the invention. Accordingly, the drawing and descriptionare to be regarded as illustrative in nature, and not as restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for illustrating the operation of a mode of thepresent invention.

FIG. 2 is another diagram for illustrating the operation of the mode ofthe present invention.

FIG. 3 is yet another diagram for illustrating the operation of the modeof the present invention.

FIG. 4 is yet another diagram for illustrating the operation of the modeof the present invention.

FIG. 5 is yet another diagram for illustrating the operation of the modeof the present invention.

FIG. 6 is a diagram for illustrating a packet communication network thataccommodates LTE.

FIG. 7 is a diagram for illustrating a packet communication network thataccommodates 2G/3G.

FIG. 8 is a diagram for illustrating a packet communication network thataccommodates LTE and 2G/3G.

FIG. 9 is a diagram for illustrating CSFB (Circuit Switch Fall Back).

FIG. 10 is a diagram for illustrating an example sequence of anexemplary embodiment 1 of the present invention.

FIG. 11 is a diagram for illustrating another example sequence of theexemplary embodiment 1 of the present invention.

FIG. 12 is a diagram for illustrating yet another example sequence ofthe exemplary embodiment 1 of the present invention.

FIG. 13 is a diagram for illustrating an example operating sequence ofan exemplary embodiment 2 of the present invention.

FIG. 14 is a diagram for illustrating another example operating sequenceof the exemplary embodiment 2 of the present invention.

FIG. 15 is a diagram for illustrating yet another example operatingsequence of the exemplary embodiment 2 of the present invention.

FIG. 16 is a diagram for illustrating an example operating sequence ofan exemplary embodiment 3 of the present invention.

FIG. 17 is a diagram for illustrating another example operating sequenceof the exemplary embodiment 3 of the present invention.

FIG. 18 is a diagram for illustrating an example operating sequence ofan exemplary embodiment 4 of the present invention.

FIG. 19 is a diagram for illustrating another example operating sequenceof the exemplary embodiment 4 of the present invention.

FIG. 20 is a diagram for illustrating yet another example operatingsequence of the exemplary embodiment 4 of the present invention.

FIG. 21 is a diagram for illustrating an example operating sequence ofan exemplary embodiment 5 of the present invention.

FIG. 22 is a diagram for illustrating another example operating sequenceof the exemplary embodiment 5 of the present invention.

FIG. 23 is a diagram for illustrating yet another example operatingsequence of the exemplary embodiment 5 of the present invention.

FIG. 24 is a diagram for illustrating an example operating sequence of amode of the present invention.

PREFERRED MODES

In one of preferred modes of the present invention, when a mobilitymanagement node, such as the MME/SGSN, has restarted, a bearermanagement node (S-GW) does not release all of bearers relevant to themobility management node (MME/SGSN). The bearer management node (S-GW)holds at least part of or entirety of bearers to continue a packetincoming service. That is, when the bearer management node, such as theS-GW, detects restarting of the mobility management node (MME/SGSN), thebearer management node confirms that the UE is accommodated in themobility management node (MME/SGSN). In connection with the UE,accommodated in the mobility management node (MME/SGSN), the bearermanagement node, such as S-GW, retains at least one of bearers setbetween the bearer management node (S-G and the external network, suchas PDN. By so doing, the UE is able to attach to the network, withpacket incoming from the external network (PDN) to the UE as a trigger,thereby accelerating the restoration of a communication service for theUE. In one of preferred modes of the present invention, the bearermanagement node maintains a specific bearer(s) for restoring acommunication service, and removes other bearers. In one preferred modesthe present invention, when maintaining the specific bearer, the bearermanagement node may start a timer. On timeout of the timer, the bearermanagement node may remove bearer resources that have been maintained.

In one of preferred modes of the present invention, it is possible toselect those bearers that render services of high reliability afterrestarting of the mobility management node (MME/SGSN). It is thuspossible to suppress consumption of resources of the bearer managementnode (S-GW) as well as to avoid congestion due to massive locationregistration signals.

In one of preferred modes of the present invention, the bearermanagement node S-GW maintains the location registration areainformation (TA List/RAI) of the UE, informed from the mobilitymanagement node (MME/SGSN), and the identification information (IMSI)associated with the UE. After restarting of the mobility management node(MME/SGSN), the bearer management node (S-GW) may, on receipt ofincoming data to the UE, notify the location registration areainformation (TA list/RAI) and the identification information (IMSI) tothe mobility management node (MME/SGSN). The mobility management node(MME/SGSN) may then perform paging, using the identification information(IMSI), for only the area corresponding to the location registrationarea information (TA list/RAI). By so doing, it is possible toselectively reduce an area that is paged by the base station.

FIG. 1 is a diagram for illustrating one of modes of the presentinvention. A mobility management node MME/SGSN that manages registrationinformation of a mobile station UE, notifies the location registrationinformation of the UE to an S-GW at the outset. The S-GW maintains thelocation registration information of the UE. The S-GW also maintainsbearers between the S-GW and the P-GW.

Restarting occurs at the mobility management node M E/SGSN.

When the S-GW detects, by e.g., health check, that the mobilitymanagement node (MME/SGSN) has restarted, the S-GW does not release butmaintains bearers that are set between the S-GW and the P-GW. In thiscase, in view of compatibility of the stable system restoration andavailability of communication services, it is possible for the S-GW notto release but continue to maintain those bearers that will provide forhigh availability services. These services may be exemplified bycommunication that is in need of high reliability in accordance with,e.g., of the operator policy, such as voice services provided by IMS.For example, the S-GW may not release but maintain specific S5/S8bearers between the S-GW and the P-GW, necessary for restoration ofservices initiated from the network side, and to delete all the otherS5/S8 bearers.

In an example shown in FIG. 2, when the S-GW detects, by e.g., healthcheck (GTP-echo), that the mobility management node MME/SGSN hasrestarted, the S-GW releases IMS control bearer services, among bearersset between the S-GW and the P-GW, while maintaining just the bearersused for IMS signaling. By thus applying to just specific services, itis also possible to gradually restore the MME/SGSN while overload on theentire system is avoided.

FIG. 3 is a diagram for illustrating the case of applying the presentinvention to IMS services. When packet data has arrived, using thebearer held by the S-GW, the packet incoming is notified, along with theidentifying the UE and the location registration area information,registered beforehand in the S-GW, to the MME/SGSN where the restartinghas occurred. The MME/SGSN is thus able to call (page) the UE using theIMSI and the location registration area information. The mobile stationUE that has been paged using the IMSI, performs re-registering (attach)to the MME/SGSN and re-establishes necessary bearers to receive theentirety of packet communication services. Thus, according to a mode ofthe present invention, even if the MME/SGSN restarts, service arrivalmay be notified to the UE to prompt its attachment to the MME to improveavailability of communication services.

According to a mode of the present invention, it is possible to cause aUE to attach to the network, after restarting of the MME/SGSN, with theincoming of the packet to the UE as a trigger. Packet communicationservices may instantaneously be restored to the UE whose services havebeen started by the arrival of the incoming packet.

In a mode of the present invention, just those bearers that need highreliability may be taken as bearers to be maintained according to thepresent invention. It is thus possible to suppress consumption of S-GWresources as well as congestion due to massive location registrationsignals. This operation is indispensable especially in case a UE wherepacket communication occurs periodically, as in MTC, is accommodated.The reason is that, in such case, packet communication occurs for manyUEs after restarting of the MME/SGSN, and hence the subscriberrecovering operations may occur in a burst fashion, with the packetcommunication as a trigger, thus possibly leading to congestion of thesystem in its entirety.

FIGS. 4 and 5 are diagrams showing an example in which the presentinvention is applied to CSFB. The CSFB function switches voiceorigination/incoming to 3G to render voice services employing the 3G-CSdomain even in case VoIP services are not provided on LTE. As regardsthe CSFB function, reference is to be made to Non-Patent Document 3(FIG. 7.2-1 Mobile Termination Call in idle mode).

Referring to FIG. 4, the MME notifies the UE's location registrationinformation to an MSC in advance. When the MME restarts, the MSC detectsthe restarting of the MME by e.g., health check. Referring to FIG. 5,when a call arrived from an originating side G-MSC (CS incoming), theMSC notifies the IMSI and the location registration area to the MME,which MME is able to call (page) the UE using the IMSI and the locationregistration area information.

The following describes exemplary embodiments of the present invention.FIGS. 6 to 9 show networks to which the present invention may beapplied.

<Exemplary Embodiment 1>

FIG. 6 is a diagram showing a network configuration of an exemplaryembodiment 1 of the present invention. Specifically, FIG. 6 shows apacket communication network that accommodates LTE. Referring to FIG. 6,the network includes a UE 101, a base station (eNodeB) 102, a MME 103,an HSS 106, an S-GW 104, a 9-GW 105, an external network (PDN) 108 andan IMS 109. The IMS 109 is a communication system that integrates packetswitched communication services by SIP (Session Initiation Protocol) toimplement multi-media services.

The MME 103 accommodates the eNodeB 102 by an S1-MME interface toperform UE mobility management and authentication as well as setting ofa user forwarding path. The MME 103 refers to the HSS 106 that is adatabase for managing subscriber information, through an S6a interface,to perform e.g., authentication. The MME 103 transmits/receives acontrol signal via S1-MME and S11 interfaces to set up or release theuser forwarding path on an S1-U interface between the eNodeB and theS-GW. The transport protocol at the S1-U interface between the eNodeBand the S-GW is GTP-U.

An S5/S8 interface 107 is an interface (user plane) between S-GW andP-GW. As a transport protocol, a tunneling protocol (GTP-U) or a proxymobile IP protocol (P-MIP), is set.

The S-GW 104 performs user data transmission/reception between it andthe eNodeB 102, while setting up or releasing an external PDN basedtransmission path via P-GW and S5/S8 interface 107. The P-GW 105connects to the external network (PDN) 108 over an SGi interface. Thefollowing describes an operation when the MME restarts.

<First Stage>

FIG. 10 is a sequence diagram that illustrates, as a first stage, astage of registering location registration area information of the UE inthe S-GW. In FIG. 10, the base station (eNodeB) 102 of FIG. 6 isomitted. It is premised that the UE1 has set up a radio control linkbetween it and the eNodeB. The respective steps of FIG. 10 will now bedescribed.

In a step 1 of FIG. 10, the UE1 transmits a location registrationrequest (Attach Request or TAU Request) to the MME 1. Note that, in LTE,the location of the UE in an idle (standby) mode is managed per locationregistration area information (tracking area). Each tracking areacorresponds to a location area or a routing area in 3G/UMTS, and iscomposed of one or a plurality of cells. In each of these cells, anidentifier of the tracking area to which the cell in question belongs isbroadcasted. The mobile station in an idle mode has its locationregistered in the tracking area in which the UE resides, and stores theidentifier of the tracking area in which the UE has its locationcurrently registered. When moving from one cell to another, the UEreceives the identifier of the tracking area which is broadcasted. Incase the identifier of the tracking area being broadcasted differs fromthe identifier of the tracking area, currently registered therein, theUE updates location registration. A request for update of this locationregistration is termed a ‘TAU Request’.

In a step S2 of FIG. 10, the MME 1 newly assigns the locationregistration area information (TA List) to the UE1.

In a step S3 of FIG. 10, the MME 1 informs the S-GW1 about the TA Listof the UE1 via S11 interface. The S-GW1 stores the TA List, informedfrom the MME 1, in a storage unit (memory) in the S-GW1, as theregistration information of the UE1.

It is noted that the location registration operation in the steps 1 and2 of FIG. 10 is known per se and is not directly relevant to thesubject-matter of the present invention. Hence, the operation is notexplained in detail.

<Second Stage>

FIG. 11 is a sequence diagram for illustrating, as a second stage, thestage of maintaining a bearer. In a step 1 of FIG. 11, the UE1 hasalready attached to the MME1 (an attach request has already beenissued). A variety of bearers have already been set up using S-GW1 andP-GW1.

In a step 2 of FIG. 11, the restarting of the MME1 occurs and in thisMME1, the registration information of the UE1, already attached, iserased.

In a step 3 of FIG. 11, the S-GW1 detects the restarting of the MME1,from processing such as a health check by GTP Echo processing.

In a step 4 of FIG. 11 S-GW 1 recognizes all mobile stations UE attachedto the MME 1 is confirmed that the UE1 is accommodated in the MME 1).

In case the present invention is provided for the entirety of theservices, all bearers related with the UE1 from the S-GW 1 towards theexternal network IMS 1 are maintained in the step S5 of FIG. 11.

In steps 6 and 7 of FIG. 11, in distinction from the step S5 of FIG. 11,the bearer maintaining function according to the present invention isnot provided for all services relating to the UE1, such that bearers(bearers used for IMS signaling are maintained for specific services(IMS services providing e.g., voice services).

After confirming in the step S4 of FIG. 11 that the UE1 has beenaccommodated in the MME 1, the S-GW1 further confirms, in the step 6 ofFIG. 11, whether or not there is a bearer(s) providing the IMS(bearer(s) used for IMS signaling) among the bearers owned by the UE1.In verifying the bearers used for IMS control in this manner, a QCI (QoSClass Identifier) value, which is among information elements that eachbearer has, may be used. If, in using the QCI value, it is ‘5’, forexample, the bearer may be concluded to be the bearer(s) used for IMSsignaling (IMS Signaling), in accordance with the Table 6.1.7 ofNon-Patent Document 1 (3GPP TS23.03). The bearer may then be concludedto be a control bearer used for rendering voice services.

If there is the control bearer(s) used for IMS signaling among thebearers relating to the UE1 managed by the S-GW1, only the relevantbearer(s) are maintained. The remaining bearers are locally released inaccordance with the operation in accordance with Non-Patent Document 2(3GPP TS23.007).

In case of maintaining the bearers used for IMS signaling (specifichearers), the S-G starts the operation of timer to release (remove)relevant hearer resources on timeout, in consideration of a case wherethe UE1 has already re-attached to another S-GW. This timer controls atime of maintaining the above mentioned specific hearer by the S-GW I,and becomes necessary to prevent failing to release the hearers that theS-GW I maintains. If, in the above timer, the time equivalent to thetime of a periodic location registration timer owned by the UE1 is set,the S-GW1 may wait for incoming of voice services for a necessaryminimum time interval corresponding to the time of the next periodiclocation registration request from the UE1. At this time, the fact thatthe UE1 has not been registered in the MME 1 is stored in the storageunit (memory) of the S-GW1.

In a step 7 of FIG. 11, the UE1 is not registered in the MME1 and onlythe IMS control bearer is maintained in the S-GW1 and in the P-GW1. Thiscompletes the second stage.

If the third stage, shown in FIG. 12, has not been carried outthereafter, the S-GW1 removes the entirety of bearers (IMS controlbearer resources) that the S-GW1 maintains in connection with the UE1,on timeout of the timer whose operation was started at the step S6 ofFIG. 11.

<Third Stage>

FIG. 12 is a sequence diagram showing the operation of a third stage incase a signal has arrived in the second stage from the PDN such as IMS.The following describes respective stages.

In a step 1 of FIG. 12, a notification from the IMSI, indicating theincoming of voice services to the UE1 arrives at the G-SW1.

In a step S2 of FIG. 12, the G-SW1 stores the information that the UE1is in an unregistered state due to the restarting of the MME1. Hence,the G-SW1 sends a downlink data notification (Downlink DataNotification), inclusive of the IMSI and the previously registered TAList, to the MME1, to inform the incoming of voice services (packetdata).

If, in a step S3 of FIG. 12, the UE1, having the IMSI that has beennotified, is not attached, the MME1 performs paging of the UE1 for thereceived TA List, using the IMSI. However, there is such a case wherein,in carrying out the step S3, the UE1 has already selected another S-GWand has attached to the MME1. In this case, to prompt the S-GW1 torelease the entirety of the bearers relevant to the UE1, the MME1returns a downlink data notification acknowledge (Downlink DataNotification Acknowledge) response indicating the cause that the UE1 hasalready re-attached.

In a step 4 of FIG. 12, the UE1 performs the attachment operation onreceipt of the paging employing the IMSI.

The attach operation of the UE in the step 4 of FIG. 12 is well-known tothose skilled in the art and, not directly relevant to the presentinvention. Hence, explanation of the detailed configuration is dispensedwith.

When the S-GW detects the restarting of the MME, if the tunnel (GTP-U)on the S1-U interface between the eNodeB and the S-GW is active, theS-GW releases the tunnel.

<Exemplary Embodiment 2>

As an exemplary embodiment 2 of the present invention, the followingdescribes the operation at the time of SGSN restarting in the networkconfiguration of FIG. 7. Basically, the operation of the exemplaryembodiment 2 is equivalent to the operation at the time of restarting ofMME in the exemplary embodiment 1. In the example of FIG. 7, 2G/3G isaccommodated. Specifically, the eNodeB 102 and the MME 103 of FIG. 6 arereplaced by a 2G/3G radio control apparatus (nodeB and RNC) 110 and anSGSN 111. An interface between the 2G radio control apparatus (NodeB andRNC) 110 and the SGSN 111 is Iu, an interface between the 2G/3G radiocontrol apparatus (NodeB and RNC) 110 and the S-GW 104 is S12, aninterface between the SGSN and the S-GW is S4 and an interface betweenthe SGSN 111 and the HSS 106 is an S6d/Gr.

The operation of the present exemplary embodiment may be summarized tohave three separate stages.

<First Stage>

FIG. 13 is a sequence diagram showing a stage of registering thelocation registration area information of the UE in the S-GW1, as afirst stage. The following describes respective steps.

In a step S1 of FIG. 13, the UE1 sends a location registration request(Attach Request/Routing Area Update Request) to the SGSN1. The RoutingArea Update Request is a location registration update request to theSGSN.

In a step S2 of FIG. 13, the SGSN1 newly assigns the locationregistration area information (RAI) to the UE1.

In a step 3 of FIG. 12, the SGSN1 notifies the S-GW1 of the RAI of theUE1. The S-GW1 maintains the RAI notified as the registrationinformation of the UE1.

The location registration operation of FIG. 12 is known per se amongthose skilled in the art and is not directly relevant to thesubject-matter of the present invention. Hence, the operation is notexplained in detail.

<Second Stage>

FIG. 14 is a sequence diagram for the stage of maintaining a bearer, asa second stage. The following describes respective steps.

In a step S1 of FIG. 14, the UE1 has already attached to the SGSN1, anda various types of hearers have been set up using the S-GW1 and P-GW1.

In a step 2 of FIG. 14, the processing of restarting occurs in theSGSN1. The registration information of the UE1 attached is erased.

In a step 3 of FIG. 14, the S-GW1 detects the restarting at SGSN1 byprocess such as a health check, by GTP Echo processing.

In a step S4 of FIG. 14, the S-GW1 recognizes the entirety of the mobilestations UE (it is confirmed that the UE1 is accommodated in SGSN1).

In case the present invention is applied to the entirety of services,all bearers are maintained in a step 5 of FIG. 14.

In steps 6 and 7 of FIG. 14, bearers are not maintained for the entiretyof the services, as is done in the step 5 of FIG. 11. Instead, just abearer relating to a specific service (IMS service, providing e.g.,voice services, in the following example) is maintained.

After step S4 of FIG. 14 of confirming that the UE1 is accommodated inSGSN1, the S-GW1 confirms, in a step 6 of FIG. 14, whether or not thereis the IMS signaling bearer among the bearers held by the UE1. The IMSsignaling bearer is a bearer used for IMS signaling. In determiningwhether or not a bearer in question is the IMS signaling bearer, thevalue of a QCI (QoS Class Identifier), which is one of the controlelements owned by each bearer, for example, may be used. If the QoSvalue is ‘5’, for example, a bearer in question is determined to be thebearer for IMS signaling (IMS signaling) in accordance with Table 6.1.7of Non-Patent Document 1 (3PP TS23.203). The hearer in question may thusbe determined to be a control bearer used for providing voice services.If there is such IMS signaling bearer, the S-GW1 maintains just suchbearer, and locally releases (removes) other bearers in accordance withthe operation of Non-Patent Document 1 (3GPP TS23.007).

In case the IMS signaling bearer is maintained, the operation of atimer, which on timeout releases the bearer, is started in order to takeaccount of the case where the UE1 has already attached to another S-GW1.This timer is necessary to prevent failing to release bearers that theS-GW1 maintains.

In case, in the above timer, the time equivalent to the time of aperiodic location registration timer included in the UE1 is set, theS-GW1 may wait for incoming of voice services for a necessary minimumtime corresponding to the time of the next periodic locationregistration request from the UE1. At this time, the fact that the UE1has not been registered in the SGSN1 is stored in the S-GW1.

In a step S7 of FIG. 14, the SGSN1 is in such a state that the UE1 hasnot been registered and that only the IMS control bearer is maintainedin the S-GW1 and in the P-GW1.

In case thereafter the third stage shown in FIG. 15 is not executed, theS-GW1 removes the entirety of the bearers maintained in connection withthe UE1 (IMS control bearer resources) at a timeout time point of thetimer whose operation started in the step 6 of FIG. 14.

<Third Stage>

FIG. 15 is a sequence diagram for illustrating the operation of a thirdstage in case of an incoming from PDN, such as IMS.

In a step S1 of FIG. 15, incoming notification of voice services fromIMS1 to the UE1 gets to the S-GW1.

In a step S2 of FIG. 15, the S-GW1 sends the IMSI and the downlink datanotification (Downlink Data Notification) inclusive of IMSI and RAI thathave been registered in advance to the MME to inform the incoming ofvoice services (packet data). It is because the S-GW1 stores that theUE1 in a non-registered state because of restarting of the SGSN1.

In case the UE1 that has the notified IMSI, has not attached, the SGSN1in a step S3 in FIG. 15 performs paging of the UE1, for RAI received,using the IMSI. However, there is such a case wherein, in carrying outthe step S3 of FIG. 15, the UE1 has already selected another S-GW andhas attached to the SGSN1. In this case, to prompt the S-GW1 to releasethe entirety of the bearers relevant to the UE1, the SGSN1 sends back tothe S-GW1 a downlink data notification acknowledge (Downlink DataNotification Acknowledge) response indicating the cause that the UE1 hasalready re-attached.

In a step 4 of FIG. 15, the UE1 that has received the paging employingthe IMSI performs an attachment operation. The attachment operation ofthe UE of the step S4 of FIG. 15 is known per se among those skilled inthe art and is not directly relevant to the subject-matter of thepresent invention. Hence, its detailed configuration is omitted.

<Exemplary Embodiment 3>

As an exemplary embodiment 3 of the present invention, the followingdescribes the operation in case of employing an ISR function (LTE/3Glocation registration omitting function) under the network configurationof FIG. 8. In ISR, the UE registers its location in both the MME and theSGSN. In case of switching a radio access system between LTE and 2G/3G,UE location registration is omitted as long as there is no change in thepreviously registered location registration area in LTE and that in2G/3G. FIG. 8 shows a packet communication network configurationaccommodating LTE and 2G/3G. This configuration corresponds to theconfiguration of FIG. 1 added by a 2G/3G radio control apparatus 110 andan SGSN 111 to he connected to the UE 101. The MME 103 is connected tothe SGSN 111 via an S3 interface, while the MME 103 and the SGSN 111 areconnected to the HSS 106 via an S6a interface and an S6d/Gr interface.The S-GW 104 is connected to the SGSN 111 and to the MME 103 via an S4interface and via an S11 interface.

<First Stage>

The processing of location registration for the UE1 from 2G/3G, as afirst stage, is shown in FIG. 13. FIG. 10 may apply as regards theprocessing of location registration from LTE. By these two operations,the S-GW1 maintains RAI and TA List as the location registration areainformation. The processing of location registration during the ISRoperation is known per se among those skilled in the art and is notdirectly relevant to the subject-matter of the present invention. Hence,its detailed configuration is omitted.

<Second Stage>

FIG. 16 is an example of a sequence as an operation in case ofrestarting of the MME1 of FIG. 8. FIG. 17 shows an example of a sequenceas an operation in case of restarting of the SGSN1 of FIG. 8

In a step 1 of FIG. 16, the UE1 has its location registered in the MME1,and a various types of bearers have been established using the S-GW 1and the P-GW1.

In a step 2 of FIG. 16, restarting occurs in the MME1, so that theregistration information of the UE1 in the MME1 is erased.

In a step 3 of FIG. 16, the S-GW1 detects the restarting of the MME1from processing, such as a health check by the GTP Echo processing.

In a step 4 of FIG. 16, the S-GW1 does not perform releasing of bearersbecause the S-GW1 knows that the UE1 attached to the MME1 has beenregistered using the SGSN1 and the ISR function. At this time, the factthat the UE1 is not registered in the MME1 is stored in an internalmemory of the S-GW1. However, in case the SGSN1 has already beenrestarted, the processing according to the present invention (processingof maintaining the bearer relevant to the UE1) is carried out as is theprocessing of FIG. 11.

The following describes the operation in case the SGSN1 of FIG. 8 hasrestarted.

In a step I of FIG. 17, the UE1 has its location registered in SGSN1,and a various types of bearers have already been set up using the S-GW1and the P-GW1.

In a step 3 of FIG. 17, the processing of restarting, for example,occurs in the SGSN1, and the registration information of the UE1, whichhas its location registered, is erased.

In a step 3 of FIG. 17, the S-GW1 detects the restarting of the SGSN1from processing such as a health check the by GTP Echo processing.

In a step 4 of FIG. 17, the S-GW1 does not perform bearer releasingbecause the S-GW1 knows that the UE1 attached to the MME1 has beenregistered using the MME1 and the ISR function. The non-registrationstatus of the UE1 in the SGSN1 is stored in the internal memory of theS-GW1. However, if the MME1 has already restarted, the processingaccording to the present invention (processing of maintaining the bearerrelevant to the UE1) is carried out as with the processing of FIG. 14.

<Third Stage>

FIG. 18 is a diagram showing an example of a sequence of the operationin case there is an incoming from the PDN under a condition that theMME1 of FIG. 8 has restarted, as a third stage. FIG. 19 is a diagramshowing an example of a sequence of the operation in case there is anincoming from the PDN under a condition that the SGSN1 of FIG. 8 isrestarted. FIG. 20 is a diagram showing an example of a sequence of theoperation in case there is the incoming from the PDN under a conditionthat both the MME1 and the SGSN1 of FIG. 8 are restarted.

In case there an incoming from the PDN under a condition the MME1 ofFIG. 8 is restarted, incoming notification of communication servicesfrom the PDN1 to the UE1 gets to the S-GW1 in a step 1 of FIG. 18.

In a step 2 of FIG. 18, the S-GW1 sends a normal downlink datanotification (Downlink Data Notification) to the SGSN1 to inform thearrival of the incoming of voice services (packet data).

In a step 3 of FIG. 18, the S-GW1 sends a downlink data notification(Downlink Data Notification), inclusive of the IMSI and thepre-registered TA List, to the MME1 to inform the incoming of voiceservices (packet data). It is because the S-GW1 stores thenon-registered state of the UE1 on account of the restarting of theMME1.

In a step 4 of FIG. 18, the SGSN1 performs normal paging (paging of themobile station responsive to the incoming).

In a step 5 of FIG. 18, in case the UE1 having the IMSI according to thenotification is not attached, the MME1 performs paging of the UE1, usingthe IMSI, by referring to the TA List received.

In a step 6 of FIG. 18, paging employing the IMSI is received at LTE,the UE1 performs an attachment operation.

The following describes a case wherein an incoming from the PDN isperformed under a condition the SGSN has restarted.

In a step 1 of FIG. 19, incoming notification of communication servicesfrom the PDN1 to the UE1 gets to the S-GW1.

In a step 2 of FIG. 19, the S-GW1 sends a normal downlink datanotification (Downlink Data Notification) to the MME1 to inform theincoming of voice services (packet data).

In a step 3 of FIG. 19, the S-GW1 sends a downlink data notification(Downlink Data Notification), inclusive of the IMSI and thepre-registered RAI, to the SGSM1, to inform the incoming of voiceservices (packet data). It is because the S-GW1 stores thenon-registered state of the UE1 on account of the restarting of theMME1.

In a step 4 of FIG. 18, the SGSN1 performs normal paging.

In a step 5 of FIG. 18, in case the UE1 having the IMSI according to thenotification has not attached, the SGSM1 performs the paging of the UE1,using the IMSI, by referring to the RAI received.

In a step 6 of FIG. 19, in case the paging employing the IMSI isreceived in 2G/3G, the UE1 performs an attachment operation.

The following describes a case wherein an incoming from the PDN isperformed under a condition both the MME and the SGSN have restarted.

In a step 1 of FIG. 20, incoming notification of communication servicesfrom the PDN1 to the UE1 gets to the S-GW1.

In a step 2 of FIG. 20, the S-GW1 sends a downlink data notification(Downlink Data Notification), inclusive of the IMSI and thepre-registered TA List, to the MME1 to inform the incoming of voiceservices (packet data). It is because the S-GW1 stores thenon-registered state of the UE1 on account of the restarting of theMME1.

In a step 3 of FIG. 20, the. S-GW 1 sends a downlink data notification,inclusive of the IMSI and the pre-registered TA List, to the SGSN1 toinform the incoming of voice services (packet data). It is because theS-GW1 stores the non-registered state of the UE1 which is due to therestarting of the MME1.

In a step 4 of FIG. 20, in case the UE1 having the IMSI according to thenotification is not attached, the MME1 performs paging of the UE1, usingthe IMSI, by referring to the TA List received.

In a step 5 of FIG. 20, in case the UE1 having the IMSI according to thenotification is not attached, the SGSN1 performs paging of the UE1,using the IMSI, by referring to the RAI received.

In a step 6 of FIG. 20, when receiving the paging employing the IMSI,the UE1 performs an attachment operation.

The attachment operation of the UE of the step S6 of FIGS. 11, 12 and 13is known per se among those skilled in the art and is not directlyrelevant to the subject-matter of the present invention. Hence, thedetail configuration is omitted.

<Exemplary Embodiment 4>

FIG. 9 is a diagram showing a network configuration according to afourth exemplary embodiment according to the present invention. In FIG.9, there is shown a CSFB (CS Fallback) architecture. Referring to FIG.), the network includes the UE 101, a base station (eNodeB) 102, an MME103, an HSS 106, an MSC/VLR 112, a CS network 113 and a G-MSC (gatewaymobile switch center) 114. The following describes the operation ofvoice incoming from the G-MSC 114 as an originating source to the UE 101with reference to FIG. 9.

A signal notifying the incoming is sent from the G-MSC 114 as anoriginating source to the MSC/VLR 112 via the CS network 113. TheMSC/VLR 112 identifies the corresponding MME 103 from the incominginformation to send a paging request message (Paging Request-Message) tothe MME 103. The MME 103 sends a paging signal to the UEs that reside inthe serving area. This paging signal includes information indicatingthat the paging is for CS services. The UE 101 recognizes thisinformation, that is, the information that the paging is that for CSservices, and sends a CS service request signal to the MME 103. The MME103 sends a handover command to the UE1. The UE 101 performs handover,while switching to 3G. The UE 101, which has switched to 3G, sends apaging response to the MSC/VLR 112, as a result of which the voiceservices at the mobile station to the incoming voice are started. Thefollowing describes the operation when the MME restarts.

The operation according to the present invention may be summarized tohave three separate stages.

<First Stage>

FIG. 21 is a sequence diagram showing, as a first stage, the stage ofregistering location registration area information of the UE. Thefollowing describes respective steps.

In a step 1 of FIG. 21, the UE1 makes a location registration requestfor CSFB (Attach Request, TAU Request and so forth) to the MME1.

In a step 2 of FIG. 21, the MME1 newly assigns (delivers) the locationregistration area information (TA List) to the UE1.

In a step 3 of FIG. 21, the MME I notifies the MSC1 of the TAU List ofthe UE1. The MSC1 maintains the TAU List, notified from the MME1, as theregistration information of the UE1.

The location registration operation of FIG. 21 is known per se amongthose skilled in the art and is not directly relevant to thesubject-matter of the present invention. Hence, the detailedconfiguration is omitted.

<Second Stage>

FIG. 22 is a sequence diagram showing, as a second stage, the stage ofmaintaining a bearer. The following describes respective steps.

In a step 1 of FIG. 22, the UE1 has already attached to the MME1.

In a step 2 of FIG. 22, restarting occurs in the MME1 and theregistration information of the UE1 is erased.

In a step 3 of FIG. 22, the MSC1 detects the restarting of the MME1 fromprocessing such as a health check by SCTP.

In a step 4 of FIG. 22, the MSC1 recognizes the entirety of the mobilestations UE attached to the MME1 (it is recognized that the UE1 isaccommodated in MME1). The above is the second stage.

<Third Stage>

FIG. 23 depicts an example sequence diagram showing, as a third stage,an operation sequence for the case of incoming (voice incoming or SMS,for example) via a CS domain. The following describes respective steps.

In a step I of FIG. 23, an incoming notification to the UE1 arrives atthe MSC1 by e.g., the G-MSC.

In a step 2 of FIG. 23, the MSC1 sends a paging request messageinclusive of IMSI and pre-registered TA List (SGsAP-PAGING-REQUESTmessage) to the MME1 to notify the MME1 of the incoming. It is becausethe MSC1 stores the non-registered state of the UE1 brought about byrestarting of the MME1.

In a step 3 of FIG. 23, in case the UE1 having the IMSI notified theretohas not attached, the MME1 performs a paging of the UE1, using the IMSI,for the TA List received.

However, there is such a case wherein, in carrying out the step S3 ofFIG. 23, the UE1 has already selected another MSC and has attached tothe MME1.

In this case, to prompt the MSC1 to release the entirety of the bearersrelevant to the UE1, the MME1 sends back to the MSC1 a paging rejectmessage (SGsAP-PAGING-REJECT message) indicating the cause that the UE1has already re-attached.

In a step 4 of FIG. 23, the UE1, which has received the paging that usesthe IMSI, performs an attachment operation. The attachment operation ofthe UE in the step 4 of FIG. 23 is known per se among those skilled inthe art and is not directly relevant to the subject-matter of thepresent invention. Hence, the configuration is omitted.

In the drawings of the above described exemplary embodiment, only one(P-GW1) is shown as the P-GW for simplicity of explanation. However, aplurality of P-GWs, such as P-GW2, P-GW3 or P-GWN, may he used in asimilar manner.

Another one of modes of the present invention will now he explained withreference to FIG. 24, which supplements FIG. 10, for example, and showssubscriber data re-installation by network triggered service request. Itis noted that the eNodeB is omitted in FIG. 24.

-   S1) The MME sends the latest TA-list to a relevant S-GW. That is,    the MME informs the latest TA-list on a per UE basis to one or more    S-GWs in every occurrence of mobility events. This information (TA    list) is important in case of MME failure because paging of the IMSI    for the coverage of the MME in its entirety may thereby be avoided.    Since larger numbers of eNodeBs are accommodated in one MME, the    load in the EPS system may become tremendously severe if paging is    to be performed for the entire coverage.-   S2) The MME performs restarting.-   S3) With a restart counter increased by one, a GTP Echo message    (GTP-V2 Echo response message) is sent to the entirety of the    relevant S-GWs.-   S4) The relevant S-GW detects MME failure by this GTP echo    mechanism. The S-GW is able to maintain all or selected bearers,    IMSI and the TA list. An operator is able to select a bearer based    on top-rank services (IMS) (service on top (IMS)), as a result of    which the bearer maintained may be selected only for important    services. For other (selected) bearers, the current MME restarting    mechanism is applied. If the S-GW is to maintain bearer resources,    IMSI and the TA list, the S-GW starts a timer that controls a time    interval for maintaining bearer resources, for example. On timeout    of the timer, the bearer resources maintained are removed. This    alternative is needed for such case in which, when the UE    re-attaches to a network, the S-GW in question is not selected. That    is, on timeout of the timer of the S-GW in question, the above    mentioned bearer resources maintained, for example, S5/S8 hearers,    which are specific bearers maintained, are removed on the assumption    that the UE has re-attached to the network via a S-GW different from    the S-GW in question.-   S5) DL data arrives at the P-GW from an external network (PDN).-   S6) The S-GW acquires the DL data from the P-GW.-   S7) The S-GW sends a downlink data notification message inclusive of    the IMSI and the TA list (DL data notification (IMSI, TA list)) to    the MME.-   S8) The MME starts the IMSI page ((Page (IMSI) to TAs specific in TA    list) for all of TAs of the TA list received from S-GW.-   S9) On receiving the IMSI page, the UE1 starts the attach (ATTACH)    procedure.-   S10) On receiving the attach (ATTACH) request from the UE, the MME    sends a location information update request to the HSS.-   S11) The HSS sends location information update acknowledge to the    MME.-   S12) The MME sends the ATTACH acceptance to the UE via eNodeB.

In case of detecting the restart of the MME, the S-GW maintains thebearer, IMSI or the TA list. In this manner, it is possible toinstantaneously recover communication services after restart of the MMEand after arrival of the DL data at the UE from the PDN side.

In a mode of the present invention, in case only the selected hearer isto be maintained, it is possible to suppress consumption of S-GWresources. In addition, by selecting and maintaining bearers forimportant services, communication services may instantaneously berestored for services of higher rank of importance, such as voicecommunication, on arrival of an incoming to the mobile station, afterthe restarting of the MME.

In another mode of the present invention, in case a bearer is to bemaintained by itself or together with the IMSI and the TA list, the timeinterval of the maintenance is managed by a timer. On timeout 2of thetimer, the bearer, IMSI and the TA list maintained are released. By sodoing, in case, after restart of the MME, the mobile station moves andattaches to a G-SW different from the S-GW that maintains the bearer, itis possible to prevent the S-GW that maintains the bearer frommaintaining the bearer longer than is necessary.

According to the present invention, described above, the followingeffects may be realized.

UE's communication services may be improved in availability by addingpacket incoming as a re-registration trigger of a UE registered in theMME/SGSN in which restarting occurred.

In case the present invention is applied to all services, incoming ofthe entirety of the packets may be used as a trigger for restoring theUE to the network. It may however be thought that many resources on theS-GW side are used, and that location registration events may becomeconcentrated. The S-GW1 is able to maintain the TA list and to performthe Paging processing by using the TA list. However, if it is notpossible for the S-GW to receive the TA list from the MME1, the pagingmay be performed for the whole area supervised by the MME1. In thiscase, many of the radio network side resources would be consumed.

According to the present invention, the S-GW1 is able to maintain theRAI and to perform the Paging processing by using the RAI. If it is notpossible for the S-GW1 to receive the RAI from the SGSN1, the paging maybe performed for the whole area supervised by the SGSN. In this case,many of the radio network side resources would be consumed.

The disclosures of the aforementioned Non-Patent Documents areincorporated by reference herein. The particular exemplary embodimentsor examples may be modified or adjusted within the gamut of the entiredisclosure of the present invention, inclusive of claims, based on thefundamental technical concept of the invention. Further, a various typesof combinations or selection of elements disclosed herein may be madewithin the framework of the claims. That is, the present invention maycover a wide variety of modifications or corrections that may occur tothose skilled in the art in accordance with the entire disclosure of thepresent invention, inclusive of claim and the technical concept of thepresent invention.

What is claimed is:
 1. A mobile terminal (UE) used in a mobilecommunication network that includes a mobility management node (MME orSGSN) and a serving gateway (S-GW), the mobile terminal comprising: areceiver that receives a paging from the mobile communication network,upon arrival of an incoming call destined for the mobile terminal at themobile communication network with the serving gateway (S-GW), uponrestarting of the mobility management node, maintaining a specific S5/S8bearer eligible for restoration of communication services triggered byan external network, while deleting other bearers, wherein said specificS5/S8 bearer eligible for restoration of communication services isdetermined by said serving gateway (S-GW) based on an operator policy;and a transmitter that, in response to the paging, re-attaches to themobile communication network.
 2. The mobile terminal according to claim1, wherein the S-GW detects the restarting of the MME or SGSN, from aprocessing.
 3. The mobile terminal according to claim 2, wherein saidprocessing comprises GTP Echo processing.
 4. The mobile terminalaccording to claim 1, wherein when the S-GW detects restarting of theMME or SGSN and if a tunnel (GTP-U) on an interface between an eNodeB(evolved NodeB) and the S-GW is active, then the S-GW releases saidtunnel.
 5. The mobile terminal according to claim 1, wherein, if the UEhas selected another S-GW and has attached to the MME or SGSN, then theMME or SGSN returns a Downlink Data Notification Acknowledge responseindicating the that the UE has already re-attached.
 6. The mobileterminal according to claim 5, wherein said Downlink Data NotificationAcknowledge prompts said S-GW to release one or more bearers associatedwith the UE.
 7. The mobile terminal according to claim 1, wherein, uponthe UE selecting a different S-GW, the S-GW releases one or more bearersassociated with the UE.
 8. The mobile terminal according to claim 1,wherein said specific S5/S8 bearer comprises a bearer used for IPMultimedia Subsystem (IMS) signaling.
 9. The mobile terminal accordingto claim 8, wherein the S-GW confirms whether or not there is a bearerproviding the IMS signaling from among the bearers owned by the UE. 10.The mobile terminal according to claim 1, wherein the S-GW receives anotification from an IMSI (International Mobile-Station SubscriptionIdentifier), indicating an incoming voice services to the UE.
 11. Themobile terminal according to claim 1, wherein the MME or SGSN, upondetecting that an attach procedure is completed in the mobile terminal,sends back to the serving gateway a Downlink Data NotificationAcknowledge signal.
 12. The mobile terminal according to claim 11,wherein said Downlink Data Notification Acknowledge signal comprises asignal indicating a cause of an attachment of the mobile terminal. 13.The mobile terminal according to claim 1, wherein said specificS5/S8bearer comprises a bearer used for providing a voice service. 14.The mobile terminal according to claim 1 wherein said specificS5/S8bearer comprises a control bearer.
 15. The mobile terminalaccording to claim 1, wherein said specific S5/S8 bearer is determinedbased on a QCI (QoS Class Identifier) value.
 16. A method forregistration of a mobile terminal (UE) in a mobile communication networkthat includes a mobility management node (MME or SGSN) and a servinggateway (S-GW), the method comprising: receiving, by the mobileterminal, a paging from the mobile communication network, upon arrivalof an incoming call destined for the mobile terminal at the mobilecommunication network with the serving gateway (S-GW), upon restartingof the mobility management node, maintaining a specific S5/S8 bearereligible for restoration of communication services triggered by anexternal network, while deleting other bearers, wherein said specificS5/S8 bearer eligible for restoration of communication services isdetermined by said serving gateway (S-GW) based on an operator policy;and re-attaching to the mobile communication network, by the mobileterminal, in response to the paging.